Abstract: Design reuse becomes important in improving software development process. The concept of object oriented design pattern opens the situation for software design reuse. Inhere arc barriers when instantiating the design patterns,such as implementation, documentation, composition. This paper presented a formal modeling approach based on role.Class,attribute of class,the relation between class all are treated as roles and all roles are modeled with Object-Z. This effectively resolves the barriers when instantiating the design patterns. The formal model of design pattern is also cvolved based on role. The evolution is divides into role layer evolution and pattern layer evolution. Pattern layer evolution is composed of role layer evolution. The model consistence can be verificated with formal theory prover.

Key words: Design pattern, Object-Z, Role, Evolution, Verification